1. Field of the Invention
The present invention relates to an analytical method and apparatus using a near infrared (NIR) spectroscopy which determine chemical components and physicochemical characteristics (hereinafter referred to as xe2x80x9cobject characteristicsxe2x80x9d) of blood such as red blood cells, hematocrit, hemoglobin, total protein, total cholesterol and blood sugar.
2. Description of the Relevant Art
In the art, the collected blood has been separated into blood plasma and red blood cells by centrifugal separation, and the blood plasma which is the supernatant liquid has been analyzed by an automatic blood analyzer and the like to determine the object characteristics of the blood.
Simple analytical methods which are disclosed in the National Publication of the Translated Version of PCT Application Nos. Hei 5-506171 and Hei 7-503863 are also known.
According to these methods, it is possible to determine the components of the blood, e.g. glucose concentration in the blood, by applying near infrared light to a finger or an ear to measure a reflectance spectrum without collecting blood from the human body.
The method for separating the blood into blood plasma and red blood cells to automatically analyze the blood plasma that is the supernatant liquid is lacking in promptness. Such analysis not only requires the use of many reagents, but also a great deal of skill. It is therefore a problem as an analytical method of the blood carried out on site by an unskilled operator.
On the other hand, the methods that have been disclosed in the National Publication of the Translated Version of PCT Application Nos. Hei 5-506171 and Hei 7-503863 are simple, but the blood is not measured directly. Accordingly, much noise is generated and there is a problem in measurement accuracy.
It is therefore an object of the present invention is to provide an analytical method and apparatus which can simply and precisely carry out an analysis of the object characteristics of the blood.
To attain the above-mentioned object, according to the present invention, an analytical method of analyzing blood is provided, which comprises the steps of: (a) applying near infrared light through a blood collection receptacle to a sample of the blood contained in the receptacle, (b) detecting at least one of diffusely reflected light and diffusely transmitted light from the blood sample in the blood collection receptacle using an optical sensor to measure a near infrared absorption spectrum of the blood sample, and (c) modifying the measured spectrum using a calibration equation which has been determined in advance from a spectrum measured using the steps (a) and (b) relative to blood specimens with known object characteristics, thereby determining an object characteristics of the blood sample.
According to conventional near infrared spectroscopy, near infrared light in a wavelength range of 1100 nm-2500 nm has been used. It has, therefore, been necessary to prepare a special crystal sample cell with an optical path length of 0.1-2 mm. Operations such as cleaning, drying and filling of the blood sample are therefore troublesome and require time. Further, because of the narrow optical path length, non-uniformity of the sample and existence of impurities have a great influence on measured results. However, even in the case of near infrared light, if near infrared light in a short wavelength range of 700 nm-1100 nm is used, its penetration force is 10 to 100 times as large as that in a long wavelength range (1100 nm-2500 nm). Accordingly, when the near infrared light in the short wavelength range is used, the optical path length can be maintained at a level of 1-2 cm and the blood analysis can be effectively carried out with the blood sample contained in an ordinary blood collection receptacle such as a tube or bag.
When the near infrared light is applied to an object (the blood), only a specified wavelength light is absorbed in proportion to the number of molecules out of various molecules contained in the object. The wavelength of the light absorbed varies with the structure of the molecule (kind of molecule). The blood contains various kinds of components and generates a complicated absorption phenomenon in which absorptions overlap. The near infrared absorption spectrum is obtained by plotting the absorbance (i.e. the degree to which the light is absorbed) against wavelengths.
To conduct quantitative analysis by using this near infrared absorption spectrum, a regression equation (a calibration equation) that relates a value of the object characteristics (the concentration or the characteristic value) to spectrum data is required. Usually, the spectrum of a sample of which the values of the object characteristics are known is measured. Based on the spectrum data and the object characteristics values, the calibration equation can be made by a chemometrics technique such as multiple linear regression (MLR), principal component regression (PCR) and PLS regression (PLS).
Further, to attain the above-mentioned object, according to the present invention, the apparatus for blood analysis is provided, which comprises a block provided with a housing portion for a translucent blood collection receptacle, a near infrared apparatus provided with a spectroscope for dispersing near infrared light from a source of light or from a blood sample contained in the blood collection receptacle and an optical sensor for detecting the near infrared light, light conduction means for conducting the near infrared light emitted from the light source or the spectroscope to the blood collection receptacle within the housing portion and for conducting, directly or through the spectroscope, at least one of diffusely reflected light and diffusely transmitted light from the blood sample within the blood collection receptacle to the optical sensor, and control means for outputting a measured spectrum of the blood sample to the near infrared apparatus and for modifying the measured spectrum using a calibration equation which has been determined in advance, for thereby computing object characteristics (chemical components or physiochemical characteristics) of the blood sample.
As the light source, it is preferable to use a metal halide lamp (a white light source) such as a tungsten halogen lamp because of its high intensity. A diode array is considered preferable as the optical sensor because it is easy for the diode array to be compacted and there is also some possibility that the diode array will be widely used from now on.
Further, when the monochromatic near infrared light is used as the light source, it is preferable to use a silicon detector or a lead sulfide detector that is commonly used as the optical sensor.
As the light conducting means, it is preferable to use an optical fiber (a single fiber) or an optical fiber bundle (a bundle of optical fibers).
It is also possible to realize a high precision measurement if the block is provided with a temperature control means for stabilizing the blood sample within the blood collection receptacle at a predetermined temperature.